Okay so...I am sure my Betta has popeye. I just noticed it today. He was swimming around and his one eye seemed to pop out more than the other and became noticeable when he swam in certain directions.
But the other thing he has too is that his mouth is stuck open!? None of my other Bettas have this problem, so this can't be normal. I put some Maracyn 2 in his tank since it said it treats popeye, and what not. But why is his mouth sticking open? I read online somewhere that maybe he could have something stuck in his mouth!? I am worried he might be having trouble breathing and eating...but he swims around normally, eats normally, and even makes very tiny bubble nest...so I don't know. I am still worried.
He's in a 2.5 gallon, heated tank with two plants and a decoration. I do water changes once a week.
ps. I can't get a picture up since I don't have my ipod cord with me. But I will be able to show you a picture tomorrow.

A picture will be helpful. Also, fill out the sticky at the top of this forum about your tank set up. If he doesn't seem to have trouble swimming, eating or breathing, you probably don't have to worry about something being stuck, but a picture will definitely help.

A picture will be helpful. Also, fill out the sticky at the top of this forum about your tank set up. If he doesn't seem to have trouble swimming, eating or breathing, you probably don't have to worry about something being stuck, but a picture will definitely help.

Housing
What size is your tank? 2.5 gallon
What temperature is your tank? 75
Does your tank have a filter?no
Does your tank have an air stone or other type of aeration?no
Is your tank heated? yes
What tank mates does your betta fish live with?none

Food
What type of food do you feed your betta fish? Omega One pellets and blood worms
How often do you feed your betta fish? once a day, 4-6 pellets

Maintenance
How often do you perform a water change? once a week
What percentage of the water do you change when you perform a water change? 100%
What type of additives do you add to the water when you perform a water change?multipurpose water conditioner and sometimes Aquarium salt

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia:
Nitrite:NA
Nitrate:NA
pH:NA
Hardness:NA
Alkalinity: NA

Symptoms and Treatment
How has your betta fish's appearance changed? He has popeye and his mouth is sticking open. Everything else is fine.
How has your betta fish's behavior changed?seems to rest a lot.But still swims around alot
When did you start noticing the symptoms? Yesterday
Have you started treating your fish? If so, how? Yes, with maracyn 2
Does your fish have any history of being ill? no. He was healthy from day one
How old is your fish (approximately)? only a few months.

PS i am watching him right now and he is resting on a plant that is closest to the surface. Like he needs the help to get air? He is resting very close to the surface of the water. I'm getting worried he might be having trouble breathing!

First of all, you need to be doing more water changes. In a tank that small, you should be doing 2-3 water changes a week - not all have to be 100%. Here is a helpful link on how much and how often you should change the water based on the tank size: http://www.bettafish.com/showthread.php?t=115758

Second, you should get a water testing kit to test for ammonia - ammonia can cause health problems such as popeye, lethargy, and difficulty breathing. Ammonia levels should always be at 0, anything higher requires a water change immediately.

Epsom salts will help with swelling. Put in 1/2 teaspoon per gallon (dissolve it first). You can do less than that to start with if you'd like. Daily partial water changes with the epsom salts would be a good idea for a few days.

The tank is heated, but it should be warmer, if it is adjustable, turn it up by one degree. 76-78 is a good minimum temperature for healthy Bettas. If not, he will probably be ok until you can get an adjustable heater.

Your betta may have injured its eye and gotten an infection also. My betta got a sudden bad case of popeye and I put him in QT and daily did about 70% water change and added dissolved epsom salt. He perked up the first day and I could see the swelling going down pretty fast. I kept it up for 2 weeks, which was a few days after he seemed fully recovered just to be certain.